Process and apparatus for the preparation of polymer solution

ABSTRACT

A process for the preparation of a polymer solution comprises the steps of: mixing a polymer with a solvent to swell the polymer in the solvent; cooling the swelled mixture to a temperature of −100 to −10° C.; and then warming the cooled mixture to a temperature of 0 to 120° C. to dissolve the polymer in the solvent. According to the present invention, the swelled mixture is cooled at a rate of faster than 1° C. per minute, or the cooled mixture is warmed at a rate of faster than 1° C. per minute. Apparatuses for the preparation of a polymer solution are also disclosed.

FIELD OF THE INVENTION

[0001] The present invention relates to a process and an apparatus forthe preparation of a polymer solution.

BACKGROUND OF THE INVENTION

[0002] Polymers have been used in various technical fields. A polymermaterial such as a plastic film is formed by using a melt or solution ofa polymer. A process of forming a polymer material comprises dissolvinga polymer in a solvent to form a solution, forming a polymer material byusing the solution, and drying the formed material by evaporating thesolvent.

[0003] The solvent of a polymer is a liquid that can dissolve a polymerat a required concentration. The solvent also requires safety and anappropriate boiling point for evaporating the solvent from a formedpolymer material. Recently, the solvent particularly requires safety ofthe human body and the environment. Therefore, it is now ratherdifficult to find out an appropriate solvent in liquids that candissolve a polymer.

[0004] For example, methylene chloride has been used as a solvent ofcellulose triacetate. However, the use of hydrocarbon halides such asmethylene chloride has recently been restricted severely to protect theglobal environmental conditions. Further, methylene chloride may causeproblems in the working environment.

[0005] On the other hand, acetone is a widely used organic solvent.Acetone has an appropriate boiling point (56° C.). Further, acetone hasfew problems on the human body and the global environmental conditions,compared with the other organic solvents. However, cellulose triacetatehas a poor solubility in acetone. Cellulose triacetate can be swelled inacetone, but is scarcely dissolved in acetone.

[0006] J. M. G. Cowie et al. report in Makromol., Chem., 143 (1971)105-114, that cellulose acetate having a substitution degree in therange of 2.70 (acetic acid content: 60.1%) to 2.80 (acetic acid content:61.3%) is dissolved in acetone by a specific process. The processcomprises the steps of cooling the cellulose acetate in acetone to atemperature of −80 to −70° C., and warming it to obtain 0.5 to 5 wt. %solution of the cellulose acetate in acetone. The method of cooling amixture of a polymer and a solvent to obtain a solution is hereinafterreferred to as a cooling dissolution method.

[0007] The solution of cellulose acetate in acetone is also reported byK. Kamide et al., Textile Machinery Society, Vol. 34, 57-61 (1981). Thereport (written in Japanese) is entitled “Dry spinning process usingacetone solution of triacetyl cellulose.” In the report, the coolingdissolution method is applied to the art of fiber spinning. Theexperiments shown in the report examine the mechanical strength, thedyeing property and the cross sectional profile of the fiber obtained bythe cooling dissolution method. In the report, 10 to 25 wt. % solutionof cellulose acetate is used to form a fiber.

SUMMARY OF THE INVENTION

[0008] An object of the present invention is to dissolve a polymer in asolvent according to an improved cooling dissolution method, even if thepolymer is swelled in, but is not dissolved in the solvent by aconventional dissolution method.

[0009] Another object of the invention is to provide an apparatus thatcan be advantageously used in a cooling dissolution method.

[0010] The present invention provides a process for the preparation of apolymer solution which comprises the steps of: mixing a polymer with asolvent to swell the polymer in the solvent; cooling the swelled mixtureto a temperature of −100 to −10° C. at a rate of faster than 1° C. perminute; and then warming the cooled mixture to a temperature of 0 to120° C. to dissolve the polymer in the solvent.

[0011] The present invention also provides a process for the preparationof a polymer solution which comprises the steps of: mixing a polymerwith a solvent to swell the polymer in the solvent; cooling the swelledmixture to a temperature of −100 to −10° C.; and then warming the cooledmixture to a temperature of 0 to 120° C. at a rate of faster than 1° C.per minute to dissolve the polymer in the solvent.

[0012] The invention further provides an apparatus for the preparationof a polymer solution which comprises a stirring device, a coolingdevice connected to the stirring device, and a warming device connectedto the cooling device, wherein both of the cooling device and thewarming device include a rotary screw.

[0013] The invention furthermore provides an apparatus for thepreparation of a polymer solution which comprises a stirring device, anextrusion device connected to the stirring device, a cooling deviceconnected to the extrusion device and a warming device connected to thecooling device, wherein the extrusion device is a fiber or membraneextruding die, and both of the cooling device and the warming devicemainly consist of a vessel.

[0014] A polymer can be dissolved in a solvent by a cooling dissolutionmethod, even if the polymer is not dissolved in the solvent by aconventional dissolution method. It has been considered that the effectof the cooling dissolution method is obtained by a change of a molecularstructure of a polymer molecule (e.g., destruction of an orderedstructure of the molecule), which is caused by cooling and warming thepolymer.

[0015] The present inventors have studied the cooling dissolutionmethod, and have found that a polymer can more easily be dissolved in asolvent by cooling or warming the polymer quickly after swelling thepolymer in the solvent. The inventors consider that a molecularstructure of a polymer molecule is greatly changed by cooling or warmingthe polymer quickly (preferably cooling and warming the polymerquickly).

[0016] J. M. G. Cowie et al. are silent with respect to the cooling rateand the warming rate, except that acetone solutions of cellulose acetateare cooled to about 240° K and allowed to warm up at a rate ofapproximately 0.2° per minute at a preliminary experiment of J. M. G.Cowie et al. K. Kamide et al. describe that the polymer cooled at −70°C. is warmed to 50° C. for 5 hours. Accordingly, the warming ratedescribed in K. Kamide et al. is 0.4° C. per minute. The cooling rate(which is not described in J. M. G. Cowie et al. and K. Kamide et al.)is supposed to be analogous to the warming rate.

[0017] In the process of the present invention, the swelled mixture iscooled at a rate of faster than 1° C. per minute or the cooled mixtureis warmed at a rate of faster than 1° C. per minute. According to theprocess of the invention, a polymer solution can be made from variouscombinations of polymers and solvents. Accordingly, the number ofsolvents that can dissolve a polymer is increased by the presentinvention. Therefore, an appropriate solvent can be selected from manyliquids that dissolve a polymer according to the process of theinvention.

[0018] The process of the invention can be advantageously conducted byusing an apparatus of the present invention, which can quickly cool orwarm a mixture of a polymer and a solvent. The apparatus of theinvention has another advantage of an excellent thermal efficiency.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019]FIG. 1 is a flow chart schematically illustrating the process andapparatus of the first embodiment.

[0020]FIG. 2 is a sectional view schematically illustrating the coolingdevice of the first embodiment.

[0021]FIG. 3 is a flow chart schematically illustrating the process andapparatus of the second embodiment.

[0022]FIG. 4 is a sectional view schematically illustrating theapparatus of the second embodiment.

DETAILED DESCRIPTION OF THE INVENTION

[0023] [Polymer and Solvent]

[0024] A combination of a polymer and a solvent is selected preferablyon a condition that the polymer is swelled in the solvent at atemperature of 0 to 120° C., and preferably 0 to 55° C. (morepreferably, a temperature at which the obtained solution will be used).If a polymer is not swelled in a solvent, it is substantially impossibleto dissolve the polymer in the solvent even if a cooling dissolutionmethod is used. Even though a polymer is dissolved in a solvent at roomtemperature, the present invention is effective because the process ofthe invention can dissolve the polymer in the solvent faster than aconventional dissolution method such as a method of stirring a mixtureof the polymer and the solvent at a room temperature or an elevatedtemperature.

[0025] Examples of the polymers include polyamides, polyolefins (e.g., anorbornene polymer), polystyrenes, polycarbonates, polysulfones,polyacrylic polymers, polymethacrylic polymers (e.g., polymethylmethacrylate), polyetheretherketones, polyvinyl alcohols, polyvinylacetates and cellulose derivatives (e.g., a cellulose ester of a lowerfatty acid).

[0026] The present invention is particularly effective in dissolving acellulose ester of a lower fatty acid in a solvent.

[0027] The lower fatty acid of the cellulose ester means a fatty acidhaving 1 to 6 carbon atoms. The number of the carbon atoms preferably is2 (cellulose acetate), 3 (cellulose propionate) or 4 (cellulosebutyrate). Cellulose acetate is more preferred, and cellulose triacetate(average acetic acid content: 58.0 to 62.5%) is particularly preferred.The invention is also effective in dissolving a cellulose ester of twoor more fatty acids, such as cellulose acetate propionate and celluloseacetate butyrate.

[0028] In the present invention, an organic solvent is preferred to aninorganic solvent. Examples of the organic solvents include ketones(e.g., acetone, methyl ethyl ketone, cyclohexanone), esters (e.g.,methyl formate, methyl acetate, ethyl acetate, amyl acetate, butylacetate), ethers (e.g., dioxane, dioxolane, THF, diethyl ether, methylt-butyl ether), hydrocarbons (e.g., benzene, toluene, xylene, hexane)and alcohols (e.g., methanol, ethanol).

[0029] A polymer is preferably swelled in a solvent, as is mentionedabove. Accordingly, the solvent should be determined depending on thepolymer. For example, preferred solvents of cellulose triacetate,polycarbonates and polystyrenes include acetone and methyl acetate.Preferred solvents of a norbornene polymer include benzene, toluene,xylene, hexane, acetone and methyl ethyl ketone. Preferred solvents ofpolymethyl methacrylate include acetone, methyl ethyl ketone, methylacetate, butyl acetate and methanol. Two or more solvents can be used incombination.

[0030] The solvent has a boiling point preferably in the range of 20 to300° C., more preferably in the range of 30 to 200° C., and mostpreferably in the range of 40 to 100° C.

[0031] [Swelling Stage]

[0032] At the first stage, a polymer is mixed with a solvent to swellthe polymer in the solvent. The swelling stage is preferably conductedat a temperature of −10 to 55° C. The swelling stage is usuallyconducted at room temperature.

[0033] The ratio of the polymer to the mixture is determined dependingon a concentration of a solution to be obtained. In the case that asolvent is supplied to the mixture at a cooling stage (described below),the amount of the solvent in the mixture should be determined bysubtracting the amount of the supplemental solvent from the amount ofthe solvent in a solution to be obtained. The amount of the polymer inthe solution to be obtained is preferably in the range of 5 to 30 wt. %,more preferably in the range of 8 to 20 wt. %, and most preferably inthe range of 10 to 15 wt. %.

[0034] The mixture of the polymer and the solvent is preferably stirredto swell the polymer in the solvent. The stirring time is preferably inthe range of 10 to 150 minutes, and more preferably in the range of 20to 120 minutes.

[0035] At the swelling stage, other optional additives such as aplasticizer, a deterioration inhibitor, a dye and an ultravioletabsorbent can be added to the polymer and the solvent.

[0036] [Cooling Stage]

[0037] At the next stage, the swelled mixture is cooled to a temperatureof −100 to −10° C. The swelled mixture preferably solidifies at thecooling stage.

[0038] According to the present invention, the swelled mixture is cooledat a rate of faster than 1° C. per minute.

[0039] In the first embodiment of the cooling stage, the cooling rate isin the range of 1 to 40° C. per minute, preferably in the range of 2 to40° C. per minute, more preferably in the range of 4 to 40° C. perminute, and most preferably in the range of 8 to 40° C. per minute.

[0040] In the second embodiment of the cooling stage, the cooling rateis faster than 40° C. per minute, preferably faster than 1° C. persecond, more preferably faster than 2° C. per second, further preferablyfaster than 4° C. per second, and most preferably faster than 8° C. persecond. The cooling rate is preferably fast as possible. However, atheoretical upper limit of the cooling rate is 10,000° C. per second, atechnical upper limit is 1,000° C. per second, and a practical upperlimit is 100° C. per second.

[0041] The cooling rate means the change of temperature at the coolingstage per the time taken to complete the cooling stage. The change oftemperature means the difference between the temperature at which thecooling stage is started and the temperature at which the cooling stageis completed.

[0042] According to the first embodiment of the cooling stage, theswelled mixture is preferably cooled by incorporating the mixture into acylinder to which a cooling mean is attached, and stirring and conveyingthe mixture in the cylinder. The swelled mixture can be cooled quicklyaccording to the first embodiment.

[0043] Further, the swelled mixture can also be cooled by further mixingthe mixture with a supplemental solvent precooled at a temperature of−105 to −15° C. The supplemental solvent is precooled preferably at atemperature of −100 to −25° C., more preferably at a temperature of −95to −35° C., and most preferably at a temperature of −85 to −55° C.

[0044] The time taken to complete the cooling stage (the time taken tocool the mixture and to keep the mixture at the cooling temperature) ispreferably in the range of 10 to 300 minutes, and more preferably in therange of 20 to 200 minutes.

[0045] The cylinder used in the first embodiment is preferably sealed toprevent contamination of water, which may be caused by dew condensationat the cooling stage. Further, the time taken to complete the coolingstage can be shortened by conducting the cooling procedures under areduced pressure. A cylinder resisting pressure is preferably used toconduct the procedures under a reduced pressure.

[0046] The first embodiment of the cooling stage can be conducted in aclosed system. The closed system has an advantage (compared with an opensystem such as the second embodiment) that amounts of components used inthe system directly reflect the composition (particularly concentration)of a solution to be obtained. Accordingly, the amounts of components canbe theoretically determined from the composition of the solution to beobtained. On the other hand, the amounts of components shouldempirically be determined from experimental results if the solution isprepared in an open system.

[0047] According to the second embodiment, the swelled mixture is cooledby extruding the mixture into a liquid precooled at a temperature of−100 to −10° C. The extruded mixture is in the form of fiber having adiameter in the range of 0.1 to 20.0 mm or in the form of membranehaving a thickness in the range of 0.1 to 20.0 mm. The diameter or thethickness is preferably in the range of 0.2 to 10.0 mm. The cooling rateis inversely proportional to the square of the diameter. If a thermalconductivity of a fibrous swelled mixture is 0.2 kcal/mhr° C. and atemperature of a liquid is −50° C., the relation between the time takento cool the center of the fiber from room temperature to −45° C. (T,second) and the diameter of the fiber (D, mm) can be represented by aformula, T=D². If the diameter is 1 mm, the cooling time is 1 second,which means the cooling rate of 70° C. per second. If the diameter is 10mm, the cooling time is 100 second, which means the cooling rate of 42°C. per minute. The relation between the cooling time and the thicknessof the membrane of the swelled mixture is the same as the relationbetween the cooling time and the diameter of the fiber.

[0048] The fiber or the membrane of the swelled mixture can becontinuous (have an unlimited length) or can be cut into pieces having acertain length. The cross sectional profile of the fibrous mixture isdetermined preferably to improve efficiency of heat transfer.Accordingly, a starlike shape is preferred to a circular shape because afiber having a star-like cross sectional profile has a large surfacearea, which is effective for heat transfer.

[0049] The extrusion of the swelled mixture can be conducted by applyingpressure (including gravity) to the mixture placed on a board havingmany small holes or slits whereby the mixture passes through the holesor slits. The formed fibers or membranes are immersed in (usuallydropped into) a precooled liquid.

[0050] There is no specific limitation with respect to the liquid forcooling the mixture (except that it must be in the form of liquid at thecooling temperature). The solvent contained in the mixture can also beused as the liquid. Since the second embodiment is an open system, theliquid may be incorporated into the mixture. If the solvent of themixture is used as the liquid, the composition of the obtained polymersolution could be analogous to the composition of the mixture.Alternatively, a polymer solution can contain a liquid or a substancecontained in the liquid as a minor component by incorporating the liquidor the substance into the mixture.

[0051] According to the second embodiment, the swelled solvent can becooled in a short time, for example several seconds. The mixture can beheld at the cooling temperature. The cooling time corresponds to thetime for which the mixture passes through the precooled liquid. If theliquid flows in a vessel, the cooling time can be adjusted bycontrolling the flow rate.

[0052] The vessel used in the second embodiment is preferably sealed toprevent contamination of water, which may be caused by dew condensationat the cooling stage. Further, the time taken to complete the coolingstage can be shortened by conducting the cooling procedures under areduced pressure. A vessel resisting pressure is preferably used toconduct the procedures under a reduced pressure.

[0053] [Separating Stage]

[0054] After the second embodiment of the cooling stage, the extrudedmixture is preferably separated from the precooled liquid after coolingthe swelled mixture and before warming the cooled mixture. The fiber ormembrane of the mixture separated from the liquid can be effectivelywarmed at the next warming stage.

[0055] The extruded mixture usually solidifies at the cooling stage. Itis easy to separate a solid fiber or membrane from a liquid. Forexample, a solid fiber or membrane in a liquid can be taken out in anet. A board having small holes or slits can be used in place of thenet. The net or the board is made of a plastic or metal that is notdissolved in a precooled liquid. The mesh of the net, the diameter ofthe hole or the width of the slit should be adjusted to the diameter ofthe fiber or the thickness of the membrane to prevent the fiber ormembrane from passing through the net or the board. Further, a conveyercan separate the fiber or membrane from the liquid. The conveyertransports the fiber or membrane from a cooling device to a warmingdevice. The conveyer can be made of a net to separate the fiber ormembrane from the liquid effectively.

[0056] [Warming Stage]

[0057] The cooled mixture is warmed to a temperature of 0 to 120° C.,and preferably to a temperature of 0 to 55° C. The temperature of theobtained solution after the warming stage usually is room temperature.

[0058] According to the present invention, the swelled mixture is warmedat a rate of faster than 1° C. per minute.

[0059] In the first embodiment of the warming stage, the warming rate isin the range of 1 to 40° C. per minute, preferably in the range of 2 to40° C. per minute, more preferably in the range of 4 to 40° C. perminute, and most preferably in the range of 8 to 40° C. per minute.

[0060] In the second embodiment of the warming stage, the warming rateis faster than 40° C. per minute, preferably faster than 1° C. persecond, more preferably faster than 20° C. per second, furtherpreferably faster than 4° C. per second, and most preferably faster than8° C. per second. The warming rate is preferably fast as possible.However, a theoretical upper limit of the warming rate is 10,000° C. persecond, a technical upper limit is 1,000° C. per second, and a practicalupper limit is 100° C. per second.

[0061] The warming rate means the change of temperature at the warmingstage per the time taken to complete the warming stage. The change oftemperature means the difference between the temperature at which thewarming stage is started and the temperature at which the warming stageis completed.

[0062] According to the first embodiment of the warming stage, thecooled mixture is preferably warmed by incorporating the mixture into acylinder to which a warming mean is attached, and stirring and conveyingthe mixture in the cylinder. The cooled mixture can be warmed quicklyaccording to the first embodiment.

[0063] The time taken to complete the warming stage (the time taken towarm the mixture and to keep the mixture at the warming temperature) ispreferably in the range of 10 to 300 minutes, and more preferably in therange of 20 to 200 minutes.

[0064] The time taken to complete the warming stage can be shortened byconducting the warming procedures under a high pressure. A cylinderresisting pressure is preferably used to conduct the procedures under ahigh pressure.

[0065] The first embodiment of the warming stage can be conducted in aclosed system. The closed system has an advantage (compared with an opensystem such as the second embodiment), as is described about the coolingstage.

[0066] According to the second embodiment, the cooled mixture is warmedby immersing the mixture in a liquid prewarmed at a temperature of 0 to120° C. The mixture is in the form of fiber having a diameter in therange of 0.1 to 20.0 mm or in the form of membrane having a thickness inthe range of 0.1 to 20.0 mm. The diameter or the thickness is preferablyin the range of 0.2 to 10.0 mm. The relation between the warming timeand the diameter of the fiber or the thickness of the membrane isanalogous to the relation described about the cooling stage.

[0067] If a mixture is extruded in the form of a fiber or membrane atthe cooling stage by the second embodiment, the cooled fiber or membraneis immersed in a prewarmed liquid at the warming stage. If the coolingstage is conducted by procedures other than the second embodiment, acooled mixture is extruded in the form of a fiber or membrane, anddropped into a prewarmed liquid. The mixture can be extruded in the samemanner as is described about the second embodiment of the cooling stage.

[0068] There is no specific limitation with respect to the liquid forwarming the mixture (except that it must be in the form of liquid at thewarming temperature). The solvent contained in the mixture can also beused as the liquid. If the process is successively conducted, theprepared polymer solution can be used as the prewarmed liquid. Forexample, the fiber or membrane of the mixture is dropped into theprepared solution in a vessel to warm the fiber or membrane quickly andto change it into the solution, whereby the amount of the solution isincreased. The increased amount of the solution is recovered from thevessel.

[0069] According to the second embodiment, the cooled mixture can bewarmed in a short time, for example several seconds.

[0070] The time taken to complete the warming stage can be shortened byconducting the warming procedures under a reduced pressure. A vesselresisting pressure is preferably used to conduct the procedures under areduced pressure.

[0071] After the warming stage, a polymer solution is obtained. If apolymer is not completely dissolved in a solvent, the procedures fromthe cooling stage to the warming stage can be repeated twice or moretimes. It can be determined by observation whether a polymer iscompletely dissolved in a solvent or not.

[0072] [Post Treatment]

[0073] The prepared polymer solution can be subjected to post treatmentsuch as adjustment of concentration (or dilution), filtration,adjustment of temperature or addition of components.

[0074] The additional components are determined according to use of thepolymer solution. Examples of the representative additives include aplasticizer, a deterioration inhibitor (e.g., a peroxide decomposer, aradical inhibitor, a metal inactivator, an acid scavenger), a dye and anultraviolet absorbent.

[0075] The obtained polymer solution should be stored at a temperaturewithin a certain range to keep the state of the solution. For example,an acetone solution of cellulose triacetate prepared by a coolingdissolution method has two phase separation ranges within thetemperature of −10 to 30° C., at which the solution is usually stored.The acetone solution of cellulose triacetate should be stored at atemperature within a uniform range between the two phase separationranges.

[0076] The obtained polymer solution can be used to form various polymermaterials.

[0077] [Preparation of Polymer Film]

[0078] A polymer film can be formed by a solvent cast method using theobtained polymer solution.

[0079] The polymer solution is cast on a support, and the solvent isevaporated to form a film. Before casting the solution, theconcentration of the solution is preferably so adjusted that the solidcontent of the solution is in the range of 18 to 35 wt. %. The surfaceof the support is preferably polished to give a mirror plane. A drum ora band is used as the support. The casting and drying stages of thesolvent cast methods are described in U.S. Pat. Nos. 2,336,310,2,367,603, 2,492,078, 2,492,977, 2,492,978, 2,607,704, 2,739,069,2,739,070, British Patent Nos. 640,731, 736,892, Japanese PatentPublication Nos. 45(1970)-4554, 49(1974)-5614, Japanese PatentProvisional Publication Nos. 60(1985)-176834, 60(1985)-203430 and62(1987)-115035.

[0080] In the case that a solution of cellulose acetate is used, thesupport preferably has a surface temperature of not higher than 10° C.when the solution is cast on the support. After casting the solution,the solution is preferably dried with air for at least 2 seconds. Theformed film is peeled off the support, and the film can be further driedwith air to remove the solvent remaining in the film. The temperature ofthe air can be gradually elevated from 100 to 160° C. Theabove-mentioned method is described in Japanese Patent Publication No.5(1993)-17844. The time for casting and peeling steps can be shortenedby the method.

[0081] [Apparatus]

[0082] The apparatus of the present invention is described belowreferring to the drawings.

[0083] The first embodiment of the apparatus comprises a stirringdevice, a cooling device connected to the stirring device, and a warmingdevice connected to the cooling device, wherein both of the coolingdevice and the warming device include a rotary screw.

[0084] The stirring device preferably comprises a first vessel and astirring means contained in the first vessel. The cooling preferablycomprising a second vessel (more preferably in the form of a cylinder)connected to the first vessel, a rotary screw contained in the secondvessel and a cooling means attached to the second vessel. The warmingdevice preferably comprises a third vessel (more preferably in the formof a cylinder) connected to the second vessel, a rotary screw containedin the third vessel and a warming means attached to the third vessel.

[0085]FIG. 1 is a flow chart schematically illustrating the process andapparatus of the first embodiment.

[0086] As is shown in FIG. 1, a polymer (P) and a solvent (S1) areintroduced into a stirring tank (1) at the swelling stage. The polymerand the solvent are mixed in the tank to swell the polymer with thesolvent.

[0087] The swelled mixture is sent to a cooling device (3) by a liquidpump (2). The liquid pump (2) preferably is a snake pump, which isadvantageously used to send a viscous liquid.

[0088] The cooling device (3) comprises a cylinder connected to thestirring tank (1) through the liquid pump (2), a rotary screw (3-1)contained in the cylinder and a cooling means (3-2) attached to thecylinder. The screw (3-1) rotates in the cylinder to send the swelledmixture while shearing, mixing and cooling the mixture. The mixturecannot stay in the cylinder because the screw (3-1) scrapes the mixturefrom the inner wall of the cylinder. The cooling means (3-2) shown inFIG. 1 is in the form of a jacket of the cylinder. A refrigerant (24)flows in the jacket. The refrigerant is sent from a refrigerant tank(21). An example of the refrigerant is a mixture of methanol and water.In place of rotating the screw, the screw can be fixed, and the mixturecan be sent through the screw in the cylinder by pressure.

[0089] After cooling the swelled mixture, the refrigerant returns to thecooling tank (21). The medium is cooled in a refrigerator (22). Acooling tower (23) processes heat formed in the refrigerator.

[0090] The cooling device (3) has a means for supplying a solventprecooled at −105 to −15° C. A supplemental solvent (S2) is precooled ina cooling stock tank (19) and sent to the cylinder of the cooling device(3) by a liquid pump (20). The swelled mixture is cooled more quickly bysupplying the precooled solvent (S2) to the mixture.

[0091] The cooling device (3) is described below in more detailreferring to FIG. 2.

[0092] The swelled mixture is quickly and uniformly cooled to −100 to−10° C. in the cooling device. The cooled mixture is sent to a warmingdevice (4).

[0093] The warming device (4) is similar to the cooling device (3). Thewarming device (4) comprises a cylinder connected to the cooling device(3), a rotary screw (4-1) contained in the cylinder and a warming means(4-2) attached to the cylinder. The screw (4-1) rotates in the cylinderto send the cooled mixture while shearing, mixing and warming themixture. The mixture cannot stay in the cylinder because the screw (4-1)scrapes the mixture from the inner wall of the cylinder. The warmingmeans (4-2) shown in FIG. 1 is in the form of a jacket of the cylinder.A heating medium (26) flows in the warming means (4-2). The heatingmedium is sent from a constant temperature bath (27). An example of theheating medium is hot water. In place of rotating the screw, the screwcan be fixed, and the mixture can be sent through the screw in thecylinder by pressure.

[0094] A prewarmed solvent may be supplied to the cooled mixture in thesame manner as in the cooling device. However, the supplement of theprewarmed solvent is not effective. The solvent lacks thermalefficiency. Heat formed by rotation of the screw in the warming deviceas well as the heating medium (26) warms the cooled mixture.

[0095] After warming the cooled mixture, the heating medium and watersent from the cooling tower (23) exchange heat in a heat exchanger (25).The thermal efficiency of the apparatus is improved by the heatexchange. After the heat exchange, the heating medium returns to theconstant temperature bath (27).

[0096] The cooled mixture is quickly and uniformly warmed in the warmingdevice to dissolve a polymer in a solvent. The obtained solution is sentto a heater (6), a filter (7) and a pressure adjusting valve (8) in theorder by a liquid pump to adjust temperature, to conduct filtration andto adjust pressure.

[0097] The solution is concentrated in a concentration tank (9). Thesolution, which has been conditioned to a high temperature and a highpressure by the heater (6) and the pressure adjusting valve (8) isintroduced into the concentration tank (9) under a reduced pressure.Accordingly, the solvent of the solution is immediately evaporated underthe reduced pressure. The evaporated solvent is sent to a liquefyingdevice (18) and to the cooling stock tank (19). The liquefied solventmixed with the supplemental solvent (S2) is again sent to the cylinderof the cooling device (3) by the pump (20).

[0098] The concentrated solution is sent to a thermal controller (11)and to a stock tank (12) by a liquid pump (10).

[0099] A device of the preparation of a polymer film according to asolvent casting method is further attached to the apparatus shown inFIG. 1.

[0100] The solution in the stock tank (12) is sent to a filter (14) andto a slit die (15) by a liquid pump (13). The solution is extruded bythe die, and cast on a band support (16). The cast solution is dried andpeeled from the support to form a film (17). The film (17) is furtherdried and wound up to a roll.

[0101]FIG. 2 is a sectional view schematically illustrating the coolingdevice (3 in FIG. 1) of the first embodiment.

[0102] A swelled mixture of a polymer and a solvent is introduced into acylinder (35) at an inlet (31-1). A cooled mixture is sent to a warmingdevice from an outlet (31-2).

[0103] The cylinder further has an inlet of a precooled supplementalsolvent (32), an inlet (33-1) of a refrigerant and an outlet (33-2) ofthe refrigerant.

[0104] In the cylinder, a screw rotates around the center of a shaft(34). The screw sends the swelled mixture from the inlet (31-1) to theoutlet (31-2) while shearing, mixing and cooling the mixture. Themixture cannot stay in the cylinder because the screw scrapes themixture from the inner wall of the cylinder (35).

[0105] Spiral turbulent flow fins are attached inside a cooling means(36) in the form of a jacket, in other words outside the cylinder (35).The fins have a function of improving the cooling efficiency of arefrigerant.

[0106] The screw shaft (34) is rotated by a motor (not shown) placedoutside the cylinder (35). The inside of the cylinder (35) is under ahigh pressure. Accordingly, the connection of the cylinder (35) to theshaft (34) is sealed with a sealing compound (38) and a seal stopper(39).

[0107] The warming device (4 in FIG. 1) can be analogous to the coolingdevice shown in FIG. 2, except that the inlet of the supplementalsolvent (32) is not necessary.

[0108] The second embodiment of the apparatus comprises a stirringdevice, an extrusion device connected to the stirring device, a coolingdevice connected to the extrusion device and warming device connected tothe cooling device, wherein the extrusion device is a fiber or membraneextruding die, and both of the cooling device and the warming devicemainly consist of a vessel.

[0109] The stirring device preferably comprises a first vessel and astirring means contained in the first vessel (41). The cooling devicepreferably comprises a second vessel placed under the extruding deviceand a cooling means attached to the second vessel (58). The secondembodiment preferably further comprises a separating device between thecooling device and the warming device. The separating device preferablycomprises a conveyer, a part of which is placed inside of the secondvessel and under the extruding device, and the other part of which isplaced outside of the second vessel. The warming device preferablycomprises a third vessel (45) placed under the part of the conveyeroutside the second vessel and a warming means attached to the thirdvessel.

[0110]FIG. 3 is a flow chart schematically illustrating the process andapparatus of the second embodiment.

[0111] As is shown in FIG. 3, a polymer (P) and a solvent (S1) areintroduced into a stirring vessel (41) at the swelling stage. Thepolymer and the solvent are mixed in the vessel (41) to swell thepolymer with the solvent.

[0112] The swelled mixture is sent to a fiber extruding die (43) by aliquid pump (42 a). The liquid pump (42 a) preferably is a snake pump,which is advantageously used to send a viscous liquid.

[0113] The die (43) extrudes the swelled mixture in the form of a fiber.The fibrous swelled mixture (44) is dropped into a cooling andseparating vessel (58). The dropped fiber is immediately cooled with acooling liquid (61) in the vessel (58).

[0114] After cooling the swelled mixture, the refrigerant returns to thecooling liquid tank (60) through a filter (59). A supplemental coolingliquid (S2) is added to the returned cooling liquid (61), and the mixedcooling liquid is cooled in the tank (60). The cooling liquid is sentfrom the tank (60) to the cooling and separating vessel (58) by a pump(42 b).

[0115] The cooled fibrous mixture (44) is separated from the coolingliquid (61) and sent to a warming vessel (45).

[0116] Means for warming and stirring the fibrous mixture (44) areattached to the warming vessel (45). The vessel (45) contains a preparedpolymer solution (50) formed by warming the fibrous cooled mixture. Thepolymer solution (50) functions as a warming liquid. The fibrous cooledmixture dropped into the warming vessel (45) is immediately warmed withthe polymer solution (50) to dissolve the polymer in the solvent.

[0117] As a result, the amount of the polymer solution (45) in thewarming vessel (45) is increased. The extra amount of the solution issent from the warming vessel (45) to a liquid pump (42 c). The solutionis further sent to a heater (46), a filter (47) and a pressure adjustingvalve (48) in the order to adjust temperature, to conduct filtration andto adjust pressure.

[0118] The solution is concentrated in a concentration tank (49). Thesolution, which has been conditioned to a high pressure by the pressureadjusting valve (48) is introduced into the concentration tank (49)under a reduced pressure. Accordingly, the solvent of the solution isimmediately evaporated under the reduced pressure. The solution isfurther heated and stirred in the concentration tank. The evaporatedsolvent (S3) is recovered and reused as the solvent (S1).

[0119] The concentrated solution is sent to a thermal controller (51)and to a stock tank (52) by a liquid pump (42 d).

[0120] A device of the preparation of a polymer film according to asolvent casting method is further attached to the apparatus shown inFIG. 3.

[0121] The solution in the stock tank (52) is sent to a filter (54) andto a slit die (55) by a liquid pump (42 e). The solution is extruded bythe die, and cast on a band support (56). The cast solution is dried andpeeled from the support to form a film (57). The film (57) is furtherdried and wound up to a roll.

[0122]FIG. 4 is a sectional view schematically illustrating theapparatus of the second embodiment (3 to 5 shown in FIG. 3).

[0123] A swelled mixture of a polymer and a solvent (71) is extruded bya fiber extruding die (43). The extruded fiber (44) of the mixture isdropped into a cooling and separating vessel (58). FIGS. 3 and 4 showonly one fiber (44) for convenience of description. However, it ispossible and preferred to extrude many fibers simultaneously by using anextruding die.

[0124] The cooling and separating vessel (58) contains a cooling liquid(61). Further, a slanted conveyer belt made of a net (22) is placed inthe cooling and separating vessel (58), except that the end of the beltis placed outside the vessel. The conveyer belt is rotated by a drivingroller (63).

[0125] The dropped fiber of the mixture (44) is immediatedly cooled withthe cooling liquid (61) in the vessel (58). The cooled fiber (64) isseparated from the cooling liquid (61) while conveying the fiber on thebelt (62). The separated fiber (64) is dropped into a warming vessel(45). A guide board (65) and a scraper (66) are attached to the conveyerbelt (62). The board (65) guides the dropped fiber (44) to the conveyerbelt (62). The scraper (66) scarps the fiber adhered to the conveyerbelt (62).

[0126] An adjusting board (67) is attached to the cooling and separatingvessel (58). The board (67) can adjust the liquid level in the vessel(58) to control the time for which the dropped fiber (44) is immersed inthe cooling liquid (61). A cooling liquid (68) flowing over the board(67) is filtered by a filter (59 in FIG. 3) and cooled in a coolingliquid tank (60 in FIG. 3), and is reused as the cooling liquid (61).

[0127] The warming vessel (45) contains a prepared polymer solution(50). The polymer solution is warmed and stirred in the vessel (45). Thecooled fiber (64) drooped into the vessel (45) is immediately warmed todissolve the polymer in the solvent. An extra amount of the preparedsolution (69) is sent from the warming vessel (45) to a liquid pump (42c in FIG. 3).

EXAMPLE 1

[0128] A solution of 26 weight parts of cellulose triacetate in 74weight parts of acetone was prepared by using the apparatus shown inFIG. 1. At the swelling stage, 70 weight parts of acetone was used. Theremaining 4 weight parts of acetone was used as a supplemental solventat the cooling stage.

[0129] The obtained solution was observed to confirm that a transparentuniform solution was formed.

[0130] The processing conditions are shown below. Temperature at theswelling stage: room temperature Time of the swelling stage: 30 minutesCooling rate: 10° C. per minute Temperature of supplemental solvent:−80° C. Final cooling temperature: −75 to −65° C. Time of the coolingstage: 60 minutes Warming rate: 10° C. per minute Final warmingtemperature: 50° C. Time of the warming stage: 60 minutes

COMPARISON EXAMPLE 1

[0131] A mixture of 26 weight parts of cellulose triacetate and 74weight parts of acetone was stirred at 30° C. for 1 hour. As a result,cellulose triacetate was swelled in acetone, but was scarcely dissolvedin acetone.

[0132] The swelled mixture was cooled to −70° C. by using a mixture ofmethanol and dry ice. The cooling rate was 0.4° C. per minute. Themixture was left for 2 hours at −70° C.

[0133] The cooled mixture was warmed to 50° C. for 5 hours whilestirring the mixture. The warming rate was 0.4° C. per minute. Themixture was stirred at 50° C. for 3 hours.

[0134] As a result, most of cellulose triacetate was dissolved inacetone, however a part of cellulose triacetate was not dissolved inacetone and observed as a milky turbidity.

EXAMPLE 2

[0135] A solution of 18 weight parts of cellulose triacetate in 82weight parts of methyl acetate was prepared by using the apparatus shownin FIG. 1. At the swelling stage, 75 weight parts of methyl acetate wasused. The remaining 7 weight parts of methyl acetate was used as asupplemental solvent at the cooling stage.

[0136] The obtained solution was observed to confirm that a transparentuniform solution was formed.

[0137] The processing conditions are shown below. Temperature at theswelling stage: room temperature Time of the swelling stage: 45 minutesCooling rate: 12° C. per minute Temperature of supplemental solvent:−50° C. Final cooling temperature: −45 to −40° C. Time of the coolingstage: 40 minutes Warming rate: 8° C. per minute Final warmingtemperature: 50° C. Time of the warming stage: 50 minutes

EXAMPLE 3

[0138] A solution of 18 weight parts of cellulose triacetate in 62weight parts of methyl acetate and 20 weight parts of ethanol wasprepared by using the apparatus shown in FIG. 1. At the swelling stage,75 weight parts of the mixture of methyl acetate and ethanol was used.The remaining 7 weight parts of the mixture of methyl acetate andethanol was used as a supplemental solvent at the cooling stage.

[0139] The obtained solution was observed to confirm that a transparentuniform solution was formed.

[0140] The processing conditions are shown below. Temperature at theswelling stage: room temperature Time of the swelling stage: 60 minutesCooling rate: 12° C. per minute Temperature of supplemental solvent:−50° C. Final cooling temperature: −55 to −45° C. Time of the coolingstage: 50 minutes Warming rate: 10° C. per minute Final warmingtemperature: 50° C. Time of the warming stage: 60 minutes

EXAMPLE 4a

[0141] A solution of 28 weight parts of cellulose triacetate in 72weight parts of acetone was prepared by using the apparatus shown inFIGS. 3 and 4.

[0142] The obtained solution was observed to confirm that a transparentuniform solution was formed.

[0143] The processing conditions are shown below. Temperature at theswelling stage: room temperature Time of the swelling stage: 30 minutesDiameter of fibrous swelled mixture: 2 mm Number of extruded fibers: 500Extruded amount of swelled mixture: 20 1 per minute Cooling rate: 15° C.per second Temperature of cooling liquid: −80° C. Final coolingtemperature: −75 to −65° C. Time of the cooling stage: 4 seconds Warmingrate: 15° C. per second Final warming temperature: 50° C. Time of thewarming stage: 20 seconds

COMPARISON EXAMPLE 2

[0144] A mixture of 28 weight parts of cellulose triacetate and 72weight parts of acetone was stirred at 30° C. for 1 hour. As a result,cellulose triacetate was swelled in acetone, but was scarcely dissolvedin acetone.

[0145] The swelled mixture was cooled to −70° C. by using a mixture ofmethanol and dry ice. The cooling rate was 0.4° C. per minute. Themixture was left for 2 hours at −70° C.

[0146] The cooled mixture was warmed to 50° C. for 5 hours whilestirring the mixture. The warming rate was 0.4° C. per minute. Themixture was stirred at 50° C. for 3 hours.

[0147] As a result, most of cellulose triacetate was dissolved inacetone, however a part of cellulose triacetate was not dissolved inacetone and observed as a milky turbidity.

EXAMPLES 4b to 12d

[0148] The procedures of Example 4a were repeated except that theprocessing conditions were changed as is shown in Table 1 (4 to 12) andTable 2 (a to d) to prepare 36 (=9×4) polymer solutions including thesolution of Example 4a. The conditions not shown in Tables 1 and 2 (suchas the conditions at the swelling stage) are the same as the conditionsin Example 4a.

[0149] The obtained solutions were observed to confirm that transparentuniform solutions were formed. TABLE 1 Weight Final cooling No. %*Composition of solvent ratio temperature 4 28 Acetone 100 −75 to −65° C.5 30 Methyl acetate 100 −45 to −40° C. 6 30 Methyl acetate/ethanol 80/20−75 to −65° C. 7 18 Methyl acetate/ethanol 80/20 −45 to −40° C. 8 17MeAc/ethanol/butanol 80/15/5 −35 to −30° C. 9 17 MeAc/butanol/acetone75/20/5 −35 to −30° C. 10  17 MeAc/EtOH/cyclohexane 80/15/5 −35 to −30°C. 11  17 MeAc/ethanol/methanol 80/18/2 −35 to −30° C. 12  17MeAc/ethanol/propanol 80/15/5 −35 to −30° C.

[0150] TABLE 2 Sample Fibers of mixture Cooling stage Warming stage No.Diam. Number Amount Rate Time Rate Time a 2 mm 500 20 15 10 15 10 b 2 mm500 35 15 10 15 10 c 5 mm  80 20  2 60  2 80 d 5 mm  80 35  2 60  2 80

[0151] It should be understood that the foregoing relates to only apreferred embodiment of the invention, and that it is intended to coverall changes and modifications of the examples of the invention hereinchosen for the purposes of the disclosure, which do not constitutedepartures from the spirit and scope of the invention.

1. A process for the preparation of a polymer solution which comprises the steps of: mixing a polymer with a solvent to swell the polymer in the solvent; cooling the swelled mixture to a temperature of −100 to −10° C. at a rate of faster than 1° C. per minute; and then warming she cooled mixture to a temperature of 0 to 120° C. to dissolve the polymer in the solvent.
 2. The process as claimed in claim 1, wherein the polymer is a cellulose ester of a lower fatty acid.
 3. The process as claimed in claim 2, wherein the polymer is cellulose acetate.
 4. The process as claimed in claim 1, wherein the polymer is mixed with the solvent at a temperature of −10 to 55° C.
 5. The process as claimed in claim 1, wherein the swelled mixture is cooled at a rate of 1 to 40° C. per minute.
 6. The process as claimed in claim 5, wherein the swelled mixture is cooled by incorporating the mixture into a cylinder to which a cooling mean is attached, and stirring and conveying the mixture in the cylinder.
 7. The process as claimed in claim 5, wherein the swelled mixture is cooled by further mixing the mixture with a solvent precooled at a temperature of −105 to −15° C.
 8. The process as claimed in claim 1, wherein the swelled mixture is cooled at a rate of faster than 40° C. per minute.
 9. The process as claimed in claim 8, wherein the swelled mixture is cooled by extruding the mixture into a liquid precooled at a temperature of −100 to −10° C., said extruded mixture being in the form of fiber having a diameter in the range of 0.1 to 20.0 mm or in the form of membrane having a thickness in the range of 0.1 to 20.0 mm.
 10. The process as claimed in claim 9, wherein the extruded mixture is separated from the precooled liquid after cooling the swelled mixture and before warming the cooled mixture.
 11. A process for the preparation of a polymer solution which comprises the steps of: mixing a polymer with a solvent to swell the polymer in the solvent; cooling the swelled mixture to a temperature of −100 to −10° C.; and then warming the cooled mixture to a temperature of 0 to 120° C. at a rate of faster than 1° C. per minute to dissolve the polymer in the solvent.
 12. The process as claimed in claim 11, wherein the polymer is a cellulose ester of a lower fatty acid.
 13. The process as claimed in claim 12, wherein the polymer is cellulose acetate.
 14. The process as claimed in claim 11, wherein the polymer is mixed with the solvent at a temperature of −10 to 55° C.
 15. The process as claimed in claim 11, wherein the cooled mixture is warmed at a rate in the range of 1 to 40° C. per minute.
 16. The process as claimed in claim 15, wherein the cooled mixture is warmed by incorporating the mixture into a cylinder to which a cooling mean is attached, and stirring and conveying the mixture in the cylinder.
 17. The process as claimed in claim 11, wherein the cooled mixture is warmed at a rate of faster than 40° C. per minute.
 18. The process as claimed in claim 17, wherein the cooled mixture is warmed by immersing the mixture into a liquid prewarmed at a temperature of 0 to 120° C., said cooled mixture being in the form of fiber having a diameter in the range of 0.1 to 20.0 mm or in the form of membrane having a thickness in the range of 0.1 to 20.0 mm.
 19. The process as claimed in claim 18, wherein the process is successively conducted, and the prepared polymer solution is used as the prewarmed liquid.
 20. An apparatus for the preparation of a polymer solution which comprises a stirring device, a cooling device connected to the stirring device, and a warming device connected to the cooling device, wherein both of the cooling device and the warming device include a rotary screw.
 21. An apparatus for the preparation of a polymer solution which comprises a stirring device, an extrusion device connected to the stirring device, a cooling device connected to the extrusion device and a warming device connected to the cooling device, wherein the extrusion device is a fiber or membrane extruding die, and both of the cooling device and the warming device mainly consist of a vessel. 